DIFFERENTIAL SUSCEPTIBILITY OF LYMPHOCYTE-T AND LYMPHOCYTE-B PROLIFERATION TO CADMIUM - RELEVANCE TO ZINC REQUIREMENT IN LYMPHOCYTE-T PROLIFERATION

Effect of zinc on an inhibitory action of cadmium to mitogen-induced lymphocyte proliferation was investigated. Cadmium at concentrations below 10-mu-M selectivity inhibited concanavalin A-induced T-cell proliferation as compared with bacterial lipopolysaccharide-induced B-cell proliferation. Such differential susceptibility of T- and B-cell proliferation was not observed in the cases of other cations such as mercury, lead, nickel, molybdenum, chromium(VI) and arsenic (V). The inhibitory effect of 10-mu-M cadmium on T-cell proliferation was almost completely prevented by addition of 30-mu-M zinc to the culture medium, but was not by ferrous iron, nickel and copper. Further, cadmium exerted the same extent of inhibition even when it was added at 16 h after concanavalin A stimulation, and thereafter the inhibition gradually decreased. Correlated well with this observation, the protective effect of zinc was seen as far as it existed during the first 16 h of the mitogen stimulation. As intracellular cadmium content and a cadmium-induced metallothionein level were not changed by zinc addition, these observations strongly suggest that cadmium inhibits some zinc-dependent processes required for T-cell proliferation.